6 THE CRASPEDOTE MEDUSA OLINDIAS AND SOME OF ITS NATURAL ALLIES. 



The majority of these tentacles arise just outside the velar tentacles, and in these 

 the roots are very short; but several of them spring at various levels from the surface 

 of the exumbrella (PI. I, Figs. 1, 2), and in these the roots are not only correspond- 

 ingly long, but are accompanied by streaks of thickened ectodermal cells loaded with 

 ivory-black pigment granules. These streaks as well as the endodermal roots are 

 narrow near the circular canal, but become broader higher up, and the black streaks 

 are continued for some distance on to the free portion of the tentacles. In younger 

 specimens these exumbrellar tentacles with long roots are very few, and there is no 

 doubt that they increase with age; and the black pigment above mentioned appears 

 to be developed always in conjunction with the union of these tentacles to the exum- 

 brella; for those tentacles which arise a little above their fellows have their prox- 

 imal portion tinged with black (Fig. 1). The ectoderm of these black streaks contains 

 nettle-cells, and is the direct continuation of the marginal nettle-ring. There is 

 no objection to calling these streaks "peroniae." The number of exumbrellar ten- 

 tacles in an example 15 millimetres in diameter was 72, and in one 75 millimetres in 

 diameter 264. 



The exumbrellar tentacles have numerous elongated warts arranged across their 

 lengths, formed by tall ectodermal cells containing nettle-capsules. They are slightly 

 enlarged at the tip, where there is an elliptical patch of mucous gland-cells. The 

 terminal portions of the exumbrellar tentacles are slightly curved inwards in a charac- 

 teristic way, and the glandular patch just mentioned may be found indifferently at 

 the tip or on the oral or aboral surface of the tentacles. In the aquarium the 

 medusa has been observed to anchor itself to the bottom by means of these glands, 

 stretching out and using the exumbrellar tentacles very much in the same way as 

 the tie-ropes of a half-filled balloon. As it is a bottom species there can hardly be any 

 reasonable doubt that these tentacles are used in the same way in its natural sur- 

 roundings. The tentacles that spring from well up on the exumbrella probably 

 serve to fasten the animal to seaweeds or rocks lying over it. 



The cells of the glandular patch above mentioned are very tall, and the cytoplasm 

 contains numerous minute granules which stain well with haBmatoxylin (aqueous 

 glycerin-alum solution after Rawitz), and the secretion is usually seen forming a 

 row of rounded masses, each corresponding to a gland cell and connected with it 

 (PL III, Fig. 20). 



The endodermal roots of the exumbrellar tentacles lie directly underneath the 

 exumbrellar ectoderm, to which they are closely applied. The cells are large and 

 vacuolated, and are directly continued into the endoderm of the circular canal. On 

 the inner side of these tentacle roots there is a layer of scattered ectoderm cells. The 



